Usher syndrome is a rare genetic disease characterized by hearing loss and progressive dysfunction of the eyesight. Ultimately, it leads to a complete loss of these two sense organs. What are the causes and symptoms of the disease? What is the treatment of people struggling with Usher syndrome?

Usher syndromeisa rare genetic diseasethat leads to gradual loss of hearing and vision. It is estimated that the Usher syndrome is responsible for 3-6 percent. all cases of childhood deafness. It also occurs in 50 percent. deaf and blind adults. The incidence of Usher syndrome is estimated to be at least 4 in 100,000 people.

Usher syndrome - causes

Usher syndrome is caused by mutations in one of the 10 currently known genes responsible for the disease, i.e. MYO7A, USH1C, CDH23, PCDH15, USH1G, CIB2, USH2A, GPR98, DFNB31 and CLRN1 ( although scientists suspect that there are yet other genes responsible for the onset of the disease). These genes code for proteins important for both seeing and perceiving sounds. Mutations in these genes prevent the protein encoded by that gene from being produced or become abnormal, leading to loss of hearing and vision loss.

Usher syndrome: inheritance

Usher syndrome is inherited in an autosomal recessive manner. The term "autosomal" means that the abovementioned genes are inherited regardless of gender - both men and women can carry the gene with the mutation. The term "recessive inheritance" means that in order for a child to become ill, they must receive one copy of the defective gene from each parent. In a situation where each of the parents carries one abnormal copy of a given gene, the probability of having a child with Usher syndrome is 25%.

Parents of a sick child, even though they carry one copy of the defective gene, do not develop symptoms of the disease. Likewise, in children who received only one gene with the mutation. This is because one correct copy of the gene is enough for the level of encoded protein to be adequate and no disease will develop.

Usher syndrome: symptoms and types of Usher syndrome

The characteristic symptoms of Usher syndrome are gradual loss of hearing and vision. Loss of the ability to seeis caused by a pigmented degeneration of the retina in the eye.Pigmented retinopathycauses progressive degeneration of the retina, leading to disturbances in night vision (night blindness, night blindness) and loss of peripheral vision (lateral vision). As the disease progresses, the field of vision narrows down to only central (straight) vision, known as "tunnel vision". In some cases, central vision is further limited by clouding of the eye lens, i.e. cataract. In addition, many people with Usher syndrome also have serious problems with balance.

There are three main types of Usher syndrome, which differ in the severity of symptoms and the age at which these symptoms appear. The most commonly diagnosed are types I and II, which account for 90-95 percent of all cases (US data).

Usher syndrome - type I

  • profound bilateral hearing loss from birth;
  • visual disturbances that appear in the first decade of life and begin with vision problems after dark. Complete loss of vision occurs in early middle age;
  • imbalance;
  • there may be a delay in motor development;

Usher syndrome - type II

  • Hearing loss that is congenital or progressive with age (moderate to severe). Most children can use hearing aids and communicate orally;
  • gradual, although slower than in type one, vision loss that usually begins in the second decade of life and is initially associated with blurred vision after dark;
  • no imbalance problems;

Usher syndrome - type III

  • children with Usher syndrome type III are usually born hearing. Gradual loss of hearing begins in late childhood or adolescence, after speech development. Sick people become completely deaf only after reaching middle age;
  • eyesight problems appear in the second decade of life and begin with night blindness. In adulthood, the sick person is blind (the second or third decade of life);
  • balance problems do not always occur

Usher syndrome: diagnostics

Due to the fact that Usher's syndrome causes disturbances in as many as three areas: hearing, sight and balance, a number of tests appropriate for each sense organ are performed:

  • visual field test and electroretinogram, which measures the electrical response of the eye's retina to a light stimulus;
  • electronystagmography, which measures involuntary movementseyeballs and is used to assess the organ of equilibrium;
  • tonal audiometry, the purpose of which is to assess the hearing threshold, which allows to determine the type and degree of hearing impairment;

Confirmation of the diagnosis is based on the identification of mutations in both copies of the gene in the patient. For this purpose, molecular biology methods such as Sanger sequencing are used. It is also possible to perform tests with the use of microarrays.

This type of examination can also be performed on the fetus (for informational purposes only). However, you should take into account the risks associated with invasive prenatal testing. Performing genetic tests and determining the exact cause of the disease (what mutations and in which genes are responsible for the occurrence of Usher syndrome) is important not only for the sick person, but also for the family. It makes it possible to determine the risk of the disease recurring in the family, to forecast the course of the disease in a patient and to provide the patient with medical care early enough.

Usher syndrome: treatment

Usher's syndrome, like any genetic disease, is an incurable disease, and the patient needs the care of many specialists, including: a pediatrician, ophthalmologist, ENT specialist, psychologist, and sometimes a neurologist.

Hearing aids are used in people with Usher syndrome. It is also possible to implant a cochlear implant with a positive result. Due to the progressive loss of vision, cochlear implant surgery should be performed as soon as possible.

It is also useful to learn sign language or Braille in the early stages of life. A special Lorm alphabet has also been developed for deaf-blind people.

According to scientists at the National Eye Institute and the Foundation for Fighting Blindness in the US, high doses of vitamin A can slow retinitis pigmentosa. Based on the results of the conducted studies, they recommend that the majority of adult patients with retinitis pigmentosa should take approximately 15,000 IU (international units) of vitamin A in the form of retinol palmitate daily (under specialist supervision). A vitamin A dose greater than 15,000 IU does not bring much he alth benefits. It should also be remembered that taking large amounts of vitamin A causes side effects, such as liver damage.

Patients with Usher syndrome type I did not participate in the studies of the National Eye Institute and the Foundation for Fighting Blindness, therefore it cannot be concluded whether the administration of vitamin A in this group of patients will have therapeutic effects. Some sources say that patients should not be given vitamin A in the form of beta-carotene.However, the effects of replacing retinol palmitate with beta-carotene are unknown, as its effect has not been tested in patients with Usher syndrome.

Category:

Genetic diseases